The present invention relates to an ink-jet recording head using a piezoelectric thin film as a driving source for ink discharge, an ink-jet recording apparatus provided with this ink-jet recording head, such as an ink-jet printer used as an output equipment of a personal computer, a facsimile or a word processor, and a method for producing an ink-jet recording head. More particularly, it relates to an improvement in an electrode forming technique.
There is a piezoelectric type ink-jet recording head using piezoelectric elements formed of lead zirconate titanate as electromechanical transducer elements, driving sources for liquid or ink discharge. This recording head generally comprises a head base on which a large number of separate ink passages are formed, a diaphragm attached to the head base so as to cover all of the separate ink passages, and piezoelectric elements deposited onto respective parts on the diaphragm corresponding to the separate ink passages. An electric field is applied to the piezoelectric element to displace it, thereby pushing out ink existing in the separate ink passage through a nozzle of the separate ink passage.
As one example, International Patent Application Laid-open In Japan No. Hei. 5-504740 is present. Then, a method for producing an ink-jet recording head described in this publication will be illustrated with reference to the drawings.
As shown in FIG. 35, a silicon oxide film SID is formed on a silicon substrate SI, and a conductive layer FMF formed of a platinum, aluminum or nickel thin film as a lower electrode is formed thereon. Then, as shown in FIG. 36, a resist area DRS exposed to light by photolithography is formed on the conductive layer, and as shown in FIG. 37, an electrode pattern FML is formed by using this resist area DRS exposed to light as a mask.
Next, as shown in FIG. 38, lead zirconate titanate PEZ which is a kind of piezoelectric thin film is further formed by the sol-gel method, and subsequently, a second metal thin film SMF as an upper electrode is deposited so as to cover lead zirconate titanate PEZ. Further, a resist RS is formed so as to cover the second metal thin film SMF.
Then, a resist area DRS exposed to light is formed so that a second electrode pattern is obtained by irradiating ultraviolet light rays through a mask MSK.
Further, as shown in FIG. 39, after formation of the second electrode pattern SML, a protective film PSV is deposited onto it. Furthermore, as shown in FIG. 39, a resist is deposited onto a second main surface of the silicon substrate, and then as shown in FIG. 40, ultraviolet light rays are irradiated through a mask MSK-to form a resist area DRS exposed to light.
Then, as shown in FIG. 41, the resist is separated so as to leave the resist area DRS exposed to light, and the silicon substrate SI is subjected to anisotropic etching in a strong alkaline solution. The resist area DRS exposed to light is further separated to form ink cavity chambers CAV.
However, in the method for producing the ink-jet recording head described above, no consideration is given to formation of the first and second electrode patterns FML and SML, and the ink cavity chambers CAV at an exact position without deviation from each other. Then, in order to form the electrode patterns and the ink cavity chambers at an exactly adjusted position, photolithography with a both side exposure device is applied to the method described above.
However, patterning of the electrode of the ink-jet recording head by the photolithography method introduce the problem that the electrode is electrolytically corroded with the developing solution used when the resist exposed to light is developed, resulting in failure to form the electrode pattern.
That is, when the first electrode pattern is made of platinum and the second electrode pattern is made of a material different therefrom, and when a positive resist for photolithography is selected from the viewpoints of low cost and improved patterning accuracy for patterning of the electrode and protection of the electrode, the electrolytic corrosion phenomenon occurs between platinum and the second metal thin film due to the difference in electrochemical potential, because the developing solution for the positive resist is an alkaline electrolytic solution.
For example, when the first electrode pattern LE is platinum and the second electrode pattern is aluminum, the phenomenon occurs that hydrogen gas is produced from platinum of the first electrode to dissolve or separate aluminum of the second electrode. This electrolytic corrosion phenomenon introduces the problems that poor formation of the electrode pattern takes place in the ink-jet recording head, and further, that no piezoelectric element can be formed.
It is therefore an object of the present invention to provide an ink-jet recording head not having poor formation of an electrode pattern caused by such an electrolytic corrosion phenomenon, and an ink-jet recording apparatus provided with the same. Further, another object of the present invention is to provide a method by which it can be produced without generation of the above-mentioned electrolytic corrosion phenomenon.
On the other hand, in order to discharge a large amount of ink from a recording head, it is desirable that a diaphragm is largely displaced. For this purpose, for example, a platinum thin plate having a higher Young""s modulus is used as the first metal thin film, and a metal thin film having a lower Young""s modulus is used as the second metal thin film. An aluminum thin film has a very low Young""s modulus. Accordingly, when a voltage is applied to a piezoelectric element device, it is displaced twice or more compared with the case that the first and second metal thin films are both made of platinum.
However, when the electrochemical potential of the second metal thin film is base to that of the first metal thin film, there is the problem that the above-mentioned electrolytic corrosion phenomenon takes place in patterning the second metal thin film by photolithography, resulting in failure to obtain a good pattern of the second metal thin film.
Then, an object of the present invention is to provide an ink-jet recording head which can attain the above-mentioned object while attaining large displacement of a diaphragm, an ink-jet recording apparatus and a manufacturing method thereof.
In order to attain the above-mentioned objects, the present inventors have conducted intensive investigation. As a result, in manufacturing processes of ink-jet recording heads, the finding has been obtained that conventional poor formation of electrodes can be avoided by selecting for upper and lower electrodes such compositions that no electrolytic corrosion takes place even when positive resists are used for pattern formation of the electrodes or protection thereof and the electrodes are exposed to developing solutions for the positive resist, even if the upper electrode and the lower electrode are in conduction.
On the other hand, in the manufacturing course of the ink-jet recording heads, generation of electrolytic corrosion in the electrodes can be avoided, even if the electrodes are exposed to the developing solutions for the positive resists, and the desired compositions can be selected for the upper and lower electrodes, by keeping the upper and lower electrodes in the nonconducting state. Further, the use of negative resists for pattern formation of the electrodes or protection thereof instead of the positive resists can also prevent generation of electrolytic corrosion and select the desired compositions for the electrodes.
The present invention is characterized by a novel ink-jet recording head obtained based on such findings, and a method for producing the same.
An ink-jet recording head according to the present invention comprises a piezoelectric element device formed on a first main surface of a substrate and ink cavity chambers formed on a second main surface, the piezoelectric element device being formed by stacking a first electrode, a piezoelectric thin film and a second electrode in this order, wherein a material of the first electrode is the same as that of the second electrode in electrochemical potential. More preferably, the first and second electrodes are both formed of platinum.
Further, an ink-jet recording head according to the present invention comprises a piezoelectric element device formed on a first main surface of a substrate and ink cavity chambers formed on a second main surface, the piezoelectric element device being formed by stacking a first electrode, a piezoelectric thin film and a second electrode in this order, wherein the electrochemical potential of a material of the first electrode and that of a material of the second electrode are within a range in which no electrolytic corrosion is developed between both electrodes to a developing solution for a resist used in forming at least one of the first and second electrodes. Preferably, the electrochemical potential of the first electrode and that of the second electrode are within a range in which no electrolytic corrosion is developed to an alkaline electrolytic solution used for development of a positive resist.
Furthermore, another ink-jet recording head according to the present invention comprises a piezoelectric element device formed on a first main surface of a substrate and ink cavity chambers formed on a second main surface, the piezoelectric element device being formed by stacking a first electrode, a piezoelectric thin film and a second electrode in this order, wherein the first and second electrodes are each formed of metals different from each other in electrochemical potential, and patterns of these electrodes are formed by use of a negative resist utilizing no electrolytic solution as a developing solution.
Further, a method for producing an ink-jet recording head according to the present invention comprises the steps of forming a piezoelectric element device on a first main surface of a substrate, and forming ink cavity chambers on a second main surface, the piezoelectric element device being formed by stacking a first electrode, a piezoelectric thin film and a second electrode on the substrate in this order, and the electrodes and ink cavity chambers being formed by use of a resist so as to give specified patterns, wherein the first and second electrodes are each formed of metals different from each other in electrochemical potential, and a negative resist is utilized for formation of at least one of the patterns of the first and second electrodes so as to prevent the first and second electrodes from being directly exposed to a developing solution for a positive resist.
Furthermore, another method for producing an ink-jet recording head according to the present invention comprises the steps of forming a piezoelectric element device on a first main surface of a substrate, and forming ink cavity chambers on a second main surface, the piezoelectric element device being formed by stacking a first electrode, a piezoelectric thin film and a second electrode on the substrate in this order, and at least one of these electrodes and ink cavity chambers being patterned by use of a photoresist, wherein the first and second electrodes are stacked on the substrate so as not to be rendered conductive to each other during the course of the patterning. In a preferred embodiment, the second electrode is formed smaller than the piezoelectric thin film.
A further method for producing an ink-jet recording head according to the present invention comprises the steps of forming a piezoelectric element device on a first main surface of a substrate, and forming ink cavity chambers on a second main surface, the piezoelectric element device being formed by stacking a first electrode, a piezoelectric thin film and a second electrode on the substrate in this order, and the electrodes and ink cavity chambers being formed by use of a resist so as to give specified patterns, wherein the first and second electrodes are each formed of materials identical to each other in electrochemical potential. Preferably, the first and second electrodes are formed of the same material. More preferably, the first and second electrodes are both formed of platinum.
According to one embodiment of the invention, a method for producing an ink-jet recording head comprises the steps of forming oxide films on both surfaces of a silicon substrate, depositing a first metal thin film onto the oxide film on the first main surface of the silicon substrate, depositing a piezoelectric thin film onto the first metal thin film, forming a second metal thin film made of a material which is the same as that of the first metal thin film on the piezoelectric thin film, depositing a positive resist film onto the oxide film of the second main surface of the silicon substrate, the second main surface having no first metal thin film thereon, depositing a negative resist film onto the second metal thin film, disposing the silicon substrate between aligned first and second masks for photolithography so that the first mask and the first main surface of the silicon substrate face each other, irradiating both surfaces of the silicon substrate with light so that the surfaces are exposed to light in patterns of the first and second masks, developing the positive resist exposed to light with an alkaline solvent for patterning, developing the negative resist exposed to light with an organic solvent for patterning, depositing a positive resist onto the whole surface of the first main surface, etching the oxide film formed on the second main surface with an acidic solution by using the patterned positive resist as a mask, separating the positive resist deposited onto the whole surface of the first main surface, and etching the second metal thin film formed on the first main surface by using the patterned negative resist as a mask.
According to another embodiment of the invention, a method for producing an ink-jet recording head comprises the steps of forming oxide films on both surfaces of a silicon substrate, forming and attached a first metal thin film onto the oxide film on the first main surface of the silicon substrate, depositing a piezoelectric thin film onto the first metal thin film, forming a second metal thin film made of a material different from that of the first metal thin film on the piezoelectric thin film, depositing a positive resist film onto the oxide film of the second main surface of the silicon substrate, the second main surface having no first metal thin film thereon, depositing a first negative resist film onto the second metal thin film, disposing the silicon substrate between aligned first and second masks for photolithography so that the first mask and the first main surface of the silicon substrate face each other, irradiating both surfaces of the silicon substrate with light so that the surfaces are exposed to light in patterns of the first and second masks, developing the positive photoresist exposed to light with an alkaline solvent for patterning, developing the first negative photoresist exposed to light with an organic solvent for patterning, depositing a second negative photoresist onto the whole surface of the first main surface, etching the oxide film formed on the second main surface with an acidic solution by using the patterned positive photoresist as a mask, separating the second negative photoresist deposited onto the whole surface of the first main surface, and etching the second metal thin film formed on the first main surface by using the patterned first negative photoresist as a mask.
In addition, the present invention provides an ink-jet recording apparatus provided with the above-mentioned ink-jet recording head.